This invention relates to alumina gels and more particularly to a process for the preparation of alumina gels of controlled porosity.
Aluminas are known and widely used as absorbents, catalysts, catalyst carriers and the like.
It is well known to produce alumina by the hydrolysis of an aluminum alkoxide. Such procedures are disclosed, for example, in U.S. Pat. Nos. 2,796,326, 2,805,920, 2,899,268, 2,917,365, 2,917,366, 3,019,080, 3,264,063, 3,419,352 and 4,172,809.
In uses of the type described hereinbefore, e.g. catalysts and catalyst carriers, the physical properties of the alumina, such as surface area, purity, pore volume and pore distribution, are of considerable importance.
Thus, U.S. Pat. No. 2,917,366 discloses the production of a high surface area alumina by forming a polymeric aluminum alkoxide of a polyhydric alcohol, then subjecting the polyalkoxide to hydrolysis with water, thereby forming polymeric, hydrated aluminum oxide in the form of very small micelles, which gives upon drying and calcining an alumina gel having an extended surface area.
U.S. Pat. No. 2,805,920 discloses another method for the production of high surface area alumina. According to this patent, a high surface area alumina of good thermal stability is provided by a process involving hydrolyzing an aluminum alcoholate by means of limited amounts of water dissolved in an organic liquid, such as an alcohol, typically isopropyl alcohol. Moreover, the data in this patent indicates that the resultant alumina has pore volumes, as high as 1.4 cc/g.
According to U.S. Pat. No. 2,917,365 aluminas of high purity are obtained by hydrolyzing aluminum alcoholate with water containing a relatively small amount of beta alumina trihydrate dispersed therein.
More recently, U.S. Pat. No. 4,172,809 discloses a process for controlling the porosity of aluminas during preparation. Thus, in one aspect of the disclosed invention therein, an alumina gel is obtained by the process of the hydrolysis of an aluminum alcoholate, such as an aluminum butylate in a water or alcohol solution. The gel is then filtered and if desired, washed with a solvent capable of removing the water from the gel. The patentee states that the solvent may be an alcohol or a ketone and in general a solvent capable of forming an azeotrope with water. The alumina must then be extruded in the presence of an alcohol.
As indicated by the prior art, there is a considerable amount of interest in being able to control and influence the physical properties of alumina gels.